added should_have_indices to test for database indices

lib/shoulda/active_record_helpers.rb

@@ -522,6 +522,26 @@ def should_have_db_column(name, opts = {})
           end
         end
       end
+
+      # Ensures that there are DB indices on the given columns or tuples of columns.
+      # Also aliased to should_have_index for readability
+      #   
+      #   should_have_indices :email, :name, [:commentable_type, :commentable_id]
+      #   should_have_index :age
+      #
+      def should_have_indices(*columns)
+        table = model_class.name.tableize
+        indices = ::ActiveRecord::Base.connection.indexes(table).map(&:columns)
+
+        columns.each do |column|
+          should "have index on #{table} for #{column.inspect}" do
+            columns = [column].flatten.map(&:to_s)
+            assert_contains(indices, columns)
+          end
+        end
+      end
+
+      alias_method :should_have_index, :should_have_indices
 
       # Ensures that the model cannot be saved if one of the attributes listed is not accepted.
       #

test/rails_root/db/migrate/001_create_users.rb

@@ -5,6 +5,10 @@ def self.up
       t.column :email, :string
       t.column :age, :integer
     end
+    add_index :users, :email
+    add_index :users, :name
+    add_index :users, :age
+    add_index :users, [:email, :name]
   end
 
   def self.down

test/unit/user_test.rb

@@ -8,6 +8,9 @@ class UserTest < Test::Unit::TestCase
 
   should_have_one :address
 
+  should_have_indices :email, :name, [:email, :name]
+  should_have_index :age
+
   should_not_allow_values_for :email, "blah", "b lah"
   should_allow_values_for :email, "a@b.com", "asdf@asdf.com"
   should_ensure_length_in_range :email, 1..100